Until this century, doctors and other health workers had little in the way of effective care to offer the sick. With few exceptions, such as vaccination and digitalis, clinical care was largely ineffective or actually harmful. Since the 1930's, however, a variety of effective pharmaceutical and other interventions have been developed and introduced. Some of these have represented important advances, many have not. Acknowledgement of medicine's potential for doing harm as well as good has led to the development and refinement of methods for considering evidence on the effectiveness of interventions. Escalating costs have now made such evidence essential for coping with the economics of health and medical practices. The purpose of this conference is to consider the strengths and weaknesses of the principle means of evaluating interventions: these range from consensus among "distinguished physicians" to rigorously organized trials and over-views of related trials. Panel discussions will then consider use of such evidence in education, in utilization, and in allocation of funding among the various means of evaluating interventions.